These Slides describe about the basics of Index properties of soil, definition and relations among different index properties of soil. These will be helpful for the students of civil engineering both Diploma and Degree Level. This chapter of Index properties of soil has been depicted in very easy and lucid manner.

1. GEOTECHNICAL
ENGINEERING
PHYSICAL & INDEX
PROPERTIES OF SOIL
PREPARED BY
GOURHARI BISWAS

2. INDEX PROPERTIES OF SOILS
• Index properties are the simple physical
properties of the soils, which are used for
identification and classification of soils for
various engineering applications.
• They indicate a qualitative behaviour of soil
when subjected to various types of load.
• To determine index properties simple tests are
required. These tests are called classification
tests. The soils are classified and identified
based on index properties.
• Engineering properties of soils are those
properties which can be used for quantifying the
Engineering behaviour of soils.

3. Different Index Properties
They can be listed as given below:
1.Water content
2.Specific gravity
3.Grain size distribution
4.Plasticity properties popularly known as Atterberg limits
(Liquid limit, Plastic limit and Shrinkage limit) and their
indices like plasticity Index, Liquidity Index, Consistency
Index, Shrinkage Index.
5.In-situ density
6.Relative density
• Void ratio, porosity, degree of saturation, are not
properties of soils, but state parameters indicating the in-
situ state of soil.

4. Different Engineering Properties of Soil
1.Shear strength (Cohesion intercept and
angle of internal friction)
2.Compressibility characteristics
(compression index and coefficient of
compressibility)
3.Permeability (Coefficient of Hydraulic
conductivity)
4.Compaction characteristics (Optimum
moisture content and Maximum Dry Unit
weight)
5.Swell/Collapse potential

5. PHASE DIAGRAM OF SOIL
• Soil is not a coherent solid material like steel and
concrete, but is a particulate/granular material.
Soils, as they exist in nature, consist of solid
particles (mineral grains, rock fragments) with
water and air in the voids between the particles.
The water and air contents are readily changed
by changes in ambient conditions and location.
• As the relative proportions of the three phases
vary in any soil deposit, it is useful to consider a
soil model which will represent these phases
distinctly and properly quantify the amount of
each phase.

6. Phase Diagrams
A schematic diagram of the
three-phase system is
shown in terms of weight
and volume symbols
respectively for soil solids,
water, and air. The weight
of air can be neglected.
The soil model is given
dimensional values for the
solid, water and air
components.
Total volume, V = Vs + Vw
+ Vv

7. Phase Diagram for Fully Saturated
and Dry Soil
A phase diagram of soil indicating the masses
and volumes of air, solid, water, and voids.

8. Inter Relationship
For the purpose of engineering analysis and
design, it is necessary to express relations
between the weights and the volumes of the
three phases.
The various relations can be grouped into:
• Volume relations
• Weight relations
• Inter-relations

9. VOLUME RELATIONS
As the amounts of both water and air are variable, the
volume of solids is taken as the reference quantity. Thus,
several relational volumetric quantities may be defined. The
following are the basic volume relations:
1. Void ratio (e) is the ratio of the volume of voids (Vv) to
the volume of soil solids (Vs), and is expressed as a
decimal.
2. Porosity (n) is the ratio of the volume of voids to the total
volume of soil (V ), and is expressed as a percentage.

10. Inter relation between Void ratio and
Porosity
Void ratio and porosity are inter-related to each other as
follows:
1/n=V/Vv= (Vv+vs)/Vv
1/n= 1+ (1/e) = (1+e)/e
n=e/ (1+e) …….(a)
1/e= (1/n)-1= (1-n)/n
e=n/ (1-n)………. (b)
• In equations (a) and (b), the porosity should be
expressed as a ratio and not percentage.
• The porosity can not be smaller than 0, and can not be
greater than 1. The void ratio can be greater than 1.

11. Degree of saturation
• The pores of a soil may contain water and air. To
describe the ratio of these two the degree of
saturation S is introduced. The degree of
saturation is the ratio of the volume of water to
the volume of voids. It is denoted by ‘S’.
• S=Vw/Vv
• The degree of saturation is generally expressed
as a percentage. It is equal to zero when the soil
is absolutely dry and 100% when the soil is fully
saturated.
• For a dry soil, S = 0%, and for a fully saturated
soil, S = 100%.

12. Air Content and Percent Air Voids
Air content (ac) is the
ratio of the volume of air
(Va) to the volume of
voids.
Also, na=n ac

13. WEIGHT RELATIONS
Density is a measure of the
quantity of mass in a unit
volume of material. Unit
weight is a measure of the
weight of a unit volume of
material. Both can be used
interchangeably. The units
of density are ton/m3, kg/m3
or g/cm3. The following are
the basic weight relations:
1. Water content, which is
also called moisture content,
is the quantity of water
contained in a material,
such as soil.
Water content is
denoted by small
letter w. Here weight
of water is Ww and
weight of solids is
Ws. Its value is 0%
for dry soil and its
magnitude can
exceed 100%.

14. contd...

15. INTER RELATIONS
• It is important to quantify the state of a soil
immediately after receiving in the
laboratory and prior to commencing other
tests. The water content and unit weight
are particularly important, since they may
change during transportation and storage.
• Some physical state properties are
calculated following the practical
measurement of others. For example, dry
unit weight can be determined from bulk
unit weight and water content. The
following are some inter-relations:

16. Inter Relations

17. VOLUME-MASS RELATIONSHIPS
1. BULK MASS DENSITY : The bulk mass density
(ρ) is defined as the total mass (M) per unit volume
(V) , ρ=M/V
2. DRY MASS DENSITY : The dry mass density
(ρd) is defined as the mass of solids per unit total
volume , ρd= Ms/V
3. SATURATED MASS DENSITY : The saturated
mass density (ρsat) is the bulk density of the soil
when it is fully saturated. ρsat= Msat/V

18. contd...
4. SUBMERGED MASS DENSITY : When
the soil exists below water, it is in a
submerged condition. The submerged mass
density (ρ’) of the soil is defined as the
submerged mass per unit total volume.
ρ’= Msub/V
5.MASS DENSITY OF SOLIDS :The mass
density of solids (ρs) is equal to the ratio of
the mass of solids to the volume of solids
ρs=Ms/Vs

19. VOLUME-WEIGHT RELATIONSHIPS
1.BULK UNIT WEIGHT (γ)= W/V
2.DRY UNIT WEIGHT (γd) = Ws/V
3.SATURATED UNIT WEIGHT (γsat) =
Wsat/V
4.SUBMERGED UNIT WEIGHT (γsub or γ’)
= Wsub/V
5.UNIT WEIGHT OF SOIL SOLIDS (γs) =
Ws/Vs

20. SPECIFIC GRAVITY OF SOLIDS
• The specific gravity of soil particles (G) is
defined as the ratio of the mass of a given
volume of solids to the mass of an equal
volume of water at 4°C.
• G = ρs/ρw
• The mass density of water ρw at 4°C is
1gm/ml, 1000 kg/m3 or 1 Mg/m3

21. BASIC RELATIONSHIPS

22. Relative Density/Density Index
It is a ratio of difference between maximum void ratio and
natural void ratio to the difference between maximum void
ratio and minimum void ratio expressed in percentage.